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| The Smøla windfarm. Some of the towers have been painted, thereby seeking to reduce bird collision risk. (photo: Brukar:bsigmundg via Wikimedia Commons) |
MIGHT the accident that killed a White-throated Needletail on Harris in the Outer Hebrides in summer 2013 have been avoided?
On June 26 that year, birders looked on in horror as the mega-rare bird flew into the tower of a wind turbine, dying instantly.
In his book, Twitching by Numbers, Gary Bagnell describes watching the bird "whooshing over his head" as "the defining moment" of his twitching career .
He writes: "If Britain ever gets another twitchable one, make sure you see it as it really is the ultimate twitch".
But might the collision have been avoided if the tower had been painted black, thus making it more conspicuous?
Bird collisions with turbine rotor blades are a well-known negative consequence of windfarms, but there has been far less attention to the risk of birds colliding with the turbine towers and how to mitigate this risk.
However, data from the 68-turbine Smøla windfarm in Norway indicates that painting part of a tower a black or a dark colour creates a visual contrast which reduces the number of collisions.
Researchers found there was a 48 per cent reduction in the number of recorded carcasses of Willow Ptarmigan at the base of painted towers compared with unpainted ones.
Their report states: The family of Grouse and Ptarmigan species are known to have poorly developed vision and flight manoeuvrability.
" In addition, many such species are often active during dusk and dawn when visibility is poor.
"These characteristics all make grouse especially prone to collide with man-made objects.
Historically, carcasses of collision-victim Willow Ptarmigan (Lagopus lagopus) at the Smøla wind-power plant were often found only a few metres from the tower base
"They showed signs of direct impact with a 'wall' rather than cuts and fractures which is usual for hits by turbine blades.
"In one case, fresh blood smear and feathers was also observed on the tower base where a fresh Ptarmigan carcass had found.
"Species in the Galliforme family typically fly relatively low above ground."
Some 97 per cent (138 of 142 flights recorded) of the Willow Ptarmigan that were flushed on Smøla showed a flight-height lower than 15 metres.
Data from both autopsy and flight height indicate that grouse are more prone to collide with the turbine tower bases than the rotor blades.
Elsewhere, several black grouse (Tetrao tetrix) that were found immediately under turbines in an area in Styria, Austria, are thought to have died because of collision with tower bases and not the rotor blades, even though the cause of death was never observed directly.
Corpses were analysed by veterinarians who concluded that injuries were consistent with the birds flying into a hard surface.
Furthermore, collision between a Willow Ptarmigan and the tower base has been confirmed by an actual observation in Sweden where one individual, part of a group of 10 birds, crashed directly into the tower base at 2.7 m height above ground.
This was at 7.05am on September 25, 2011.
The report's authors conclude: "Our study shows that painting of the wind turbine tower base reduces bird collisions.
"This relatively simple and cost-effective mitigation measure should be considered in the planning of new windfarms, especially in areas where there are species in the Galliforme family and other birds with relatively poor vision and manoeuvrability and which generally perform low altitude flights."
The report was compiled by Norwegian researchers Bård G Stokke, Torgeir Nygård, Ulla Falkdalen, Hans C. Pedersen and Roel May. Their investigations were funded by the Research Council of Norway.
* Since then, the operators of the Smøla windfarm, Statkraft, have also applied black paint to a single blade on some of its turbines, resulting in fewer fatal collisions for raptors such as White-tailed Eagles.
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